Electrolytic process for refining indium



Aug. 23, 1966 A. LAVlTT 3,268,426

ELECTROLYTIC PROCESS FOR REFINING INDIUM Filed Jan. 9. 1962 IIN FIG I mpunmzs o I l O 0 PH .5 G 2 INVENTOR.

ALEXANDER LAVITT BYjwfww United States Patent 3,268,426 ELECTROLYTIC PROCESS FOR REFINING INDIUM Alexander Lavitt, Brooklyn, N.Y., assignor to Alloys Unlimited Inc., Long Island City, N.Y. Filed Jan. 9, 1962, Ser. No. 165,153 4 Claims. (Cl. 204-105) This invention relates to means and methods for refining indium, and more particularly to such means wherein the electrolyte is continuously circulated through a bed of quaternary strong base resin.

Various methods are described in the literature for the electrodeposition of indium. Cyanide, sulfamate, chloride sulfuric acid, and chloride acetic acid baths have been mentioned. Most methods furthermore used sheets of indium for a cathode, and glue or other organic additives to achieve the desired texture or adhesive qualities of the deposit.

Referring now to the present invention:

It was felt that a cathode of material other than indium, i.e., graphite, was more desirable for the following reasons:

(1) Does not require rolling and replacement.

(2) Readily obtainable and of high uniform purity.

(3) Ease of handling.

(4) Not re adily contaminated or damaged as in connecting terminals.

(5) Readily cleaned.

(6) Low in cost.

My experience showed that (a) additives could be dispensed with as only a moderate amount of adhesion was required and treeing was not objectionable if the deposition were removed daily; (b) an all chloride solution, range pH 0.5-1.0 gave a greater plating efiiciency, 95% or better, than any of the other electrolytes.

There remained the problem of reduction of impurities. Various authors had indicated that plating took place for a four or five day period of time, then the anode slime was removed and the electrolyte was treated chemically to remove or precipitate impurities.

I have found that circulating the electrolyte through a bed of quaternary strong base resin such as IRA 400 will effectively remove impurity ions, and permit continual plating until the anodes are expended.

Accordingly a principal object of the invention is to provide new and improved means and methods for refining indium.

Another object of the invention is to provide new and improved means and methods for refining indium including means for continuously circulating an electrolyte through a bed of quaternary strong base resin.

Another object of the invention is to provide new and improved means for refining indium utilizing crude indium as an anode and graphite as a cathode in an electrolytic solution of sodium chloride.

Another object of the invention is to provide new and improved means for refining indium utilizing crude indium as an anode and graphite as a cathode in an electrolytic solution of sodium chloride having a pH .51.0.

Another object of the invention is to provide new and improved means for refining indium comprising an electrolytic cell having an anode of crude indium, a cathode of graphite and an electrolyte of sodium chloride and indium tri-chloride in a solution of pH .5-1.0, and means to continuously circulate the electrolyte through a bed of quaternary strong base resin to regenerate the electrolyte by means of anion exchange.

These and other objects of the invention will be apparent from the following specification and drawings, of which FIG. 1 is a schematic diagram of apparatus for performing the process and FIG. 2 is a graph illustrative of the pH range.

The process will be described in connection with the figures.

Example 1 FIG. 1 shows an electrolytic cell 1 which may be of Plexiglas which contains an electrolytic solution of sodium chloride and indium tri-chloride. Sodium chloride is introduced at grams per liter. Hydrochloric acid is added to achieve the desired pH which has been found in the range of .51.0 as will be discussed.

On top of the tank or cell 1 is mounted a plurality of anodes 3, 4, 5, etc., which comprise plates of crude indium which contain primary impurities of lead and tin, and smaller amounts of silver, thallium, cadmium, copper, bismuth and aluminum. The anodes are suspended from insulating rack 6 which is mounted on top of the tank 1. Equally spaced between the anodes is a plurality of cathodes 7, 8, 9 which comprise plates of graphite. 'Ihe anodes are connected in parallel to the positive side of the battery 10 which is volt and the cathodes are connected in parallel to the other side of the battery 10. The current density may be of the order of 20 amps./ sq. ft.

The electrolyte solution is continuously circulated by means of the pump 11 which pumps the solution through the pipe 12, pump 11, pipe 13, column 14, pipe 15, column 16 and pipe 17 back to the other end of the tank 1. The pressure and rate of flow may be controlled by means of the bypass pipe 20 having a valve 21, which is connected to the output of the pump. A preferable rate of flow is that necessary to change the volume of the tanks every ninety minutes.

The columns 14 and 16 each contain a bed 14' and 16 of a quaternary strong base resin which fills about twothirds of the columns. At the bottom and top of each resin bed are mounted glass wool filters 22, 22' and 26, 2 3. The columns 14 and 16 are preferably made of a plastic material such as polyvinyl chloride and the pipes may be of the same material or of any equivalent material which is suitable for transmitting an acid solution.

The beds of quaternary strong base resin may comprise a commercial product such as IRA 400 Amberlite. The resin beds are treated periodically by washing them in a 4% sulphuric acid and water solution. The resin is used in the form of small round particles. Applicants theory is that the primary function of the resin is to purify the electrolytic solution by absorbing small amounts of materials such as lead from solution. The absorption of lead is believed not related to ion exchange but is believed related to chromatographic absorption. Other materials such as tin and copper are minimized by electrolytic refining The electrolyte is circulated continuously until the anodes are expended. Pure indium deposits on the graphite cathodes where it is scraped off manually, for instance daily.

It has been found that the pH range of the solution is preferably of the order of 5-1.0 for the optimum removal of lead and tin impurities.

Example 2 FIG. 2 illustrates the effect of changing the pH on the deposits of both lead and tin. It is noted that the two curves cross over in the area where the pH is from .5'1.0. Due to the fact of the cross-over of these curves the pH range is somewhat critical for removing these impurities.

The indium tri-chloride is used only to accelerate the starting of the process. It is not essential to the process.

Typical analysis of indium refined by the present process 1s:

In-99.9994% Pb-0.0002% Sn-0.0003% A g 0.0001% with no other elements detected spectrographically.

Many modifications may be made by those who desire to practice the invention without departing from the scope thereof \which is defined by the following claims.

I claim:

1. The process of refining indium comprising the steps passing an electric current through an anode of crude indium to a cathode of graphite in an electrolytic solution of sodium chloride With a pH of .51.0,

continuously passing said electrolytic solution through a bed of quaternary strong base resin, periodically passing sulfuric acid through said bed and scraping pure indium from said cathode.

2. The process of refining indium comprising the steps passing an electric current through an anode of crude indium to a cathode of graphite in an electrolytic solution of sodium chloride,

' continuously passing said electrolytic solution through a bed of quaternary strong base resin, periodically passing sulfuric acid through said bed and scraping pure indium from said cathode. 3. The process of refining indium comprising the steps of;

, passing an electric current through an anode of crude indium to a cathode of graphite in an electrolytic solution of sodium chloride, indium tri-chloride with a pH of 5 1.0, and

continuously passing said electrolytic solution through a bed of quaternary strong base resin, and periodic'ally passing sulfuric acid through said bed.

4. The process of refining indium comprising the steps of;

passing an electric current through an anode of crude indium to a cathode of graphite in an electrolytic solution of sodium chloride,

continuously passing said electrolytic solution through a bed of quaternary strong base resin, periodically passing sulfuric acid through said bed.

References Cited by the Examiner OTHER REFERENCES Diggin, American Electroplaters Monthly Review, May 1946, pp. 513-526.

JOHN H. MACK, Primary Examiner.

MURRAY TILLMAN, Examiner.

G, KAPLAN, L. G. WISE, H. M. FLOURNOY,

Assistant Examiners. 

1. THE PROCESS OF REFINING INDIUM COMPRISING THE STEPS OF; PASSING AN ELECTRIC CURRENT THROUGH AN ANODE OF CRUDE INDIUM TO A CATHODE OF GRAPHITE IN AN ELECTROLYTIC SOLUTION OF SODIUM CHLORIDE WITH A PH OF .5-1.0, CONTINUOUSLY PASSING SAID ELECTROLYTIC SOLUTION THROUGH A BED OF QUATERNARY STRONG BASE RESIN, PERIODICALLY 